1. Field of the Invention
This invention relates to a slip supply system for supplying slip to one or more casting molds in the slip casting for a piece of sanitary ware or the like. More particularly, the invention is directed to a system which allows an increase in quality of the cast-molded products of slip and an effective utilization of discharged slip.
2. Description of the Background Art
In the slip casting using a plaster mold, the number of casting operations per day is generally limited to two or three times because of the characteristics of plaster and, moreover, one or two hours are required for each casting cycle. For these reasons, a system is proposed for mass production in which, using a casting apparatus shown in FIG. 3, casting operations of slip are simultaneously performed in a plurality of casting molds, thereby ensuring the number of molded products per cycle.
This casting apparatus includes a slip supply pipe 2 laid below a plurality of casting molds 1, and pouring hoses 3 which branch off from the slip supply pipe 2 each connected to a slip supply and discharge port (not shown) of the casting mold 1 through a pouring valve 4.
A slip supply source valve 5 is provided at the upstream side of the slip supply pipe 2, and a head tank 6 for the supply of slip is connected to the upstream side thereof. Slip is supplied to the head tank 6 for the supply of slip by way of a slip main pipe 7 and a slip main pipe valve 8 from a slip supply source (not shown), and the slip main pipe valve 8 is adapted to be controlled by means of a device (not shown) for detecting a level of slip in the tank 6.
Moreover, a slip discharge valve 9 is provided at the downstream side of the slip supply pipe 2, and is further connected at the downstream side thereof to a slip discharge tank 10.
At the top of each casting mold 1 is provided a pressurized air supply port 11, to which a pressurized air supply source 14 is connected through a pressurized air pipe 13 having a pressurized air valve 12. Further, a vent valve 15 is provided in the pressurized air pipe 13.
In the casting operation of slip, the pressurized air valve 12 and the slip discharge valve 9 are first closed and, simultaneously, the slip main pipe valve 8, slip supply source valve 5, pouring valves 4 and vent valve 15 are opened. Slip is then supplied to the interior of the casting mold 1 by the head pressure (water head pressure) of the head tank 6 for the supply of slip, and a molded product is formed after the lapse of a predetermined time.
Thereafter, the slip supply source valve 5 and vent valve 15 are closed and, simultaneously, the slip discharge valve 9 is opened and the pressurized air valve 12 is further opened to thereby discharge the slip, which is not deposited to the interiors of the casting molds 1, into the slip discharge tank 10. This is called slip discharge.
After completion of the slip discharge, the pouring valves 4 are closed and, subsequently, a hardening operation is performed in such a manner that pressurized air is supplied to the interiors of the casting molds 1 for a predetermined period of time to shift the moisture of the molded products to the casting molds 1, causing the water content of the molded products to be reduced. After completion of this hardening operation, the molded products are removed from the casting molds 1 and the following cycle is carried out.
In the above-described slip supply system, the interiors of the slip supply pipe 2 and pouring hoses 3 become substantially empty after completion of the slip discharge, with slip being attached to the inner walls of the pipes. Since time is taken until the following pouring cycle, the attached slip becomes dry and solidifies and, at the time of the following casting operation, the solidified slip is peeled off by the slip supplied from the head tank 6 for the supply of slip and mixes into the slip, introducing air into the slip. Thus, the slip containing solid matter and air therein is poured into the plaster molds.
As a result, the molded product includes solid matter and pin-holes produced by the introduced air, which cause a deterioration in quality and a decrease in yield of the molded products.
Further, there is a problem in that since the solid matter also mixes into the discharged slip such discharge slip cannot be recovered and utilized as it is. The discharge slip requires a discharged slip treatment by additional equipment, thus making it impossible to effectively utilize the discharged slip.